The Iranian government, more than almost any other, censors what
citizens can read online, using elaborate technology to block millions
of Web sites offering news, commentary, videos, music and, until
recently, Facebook and YouTube. Search for “women” in Persian and
you’re told, “Dear Subscriber, access to this site is not possible.”

Last July, on popular sites that offer free downloads of various
software, an escape hatch appeared. The computer program allowed
Iranian Internet users to evade government censorship.

College students discovered the key first, then spread it through e-
mail messages and file-sharing. By late autumn more than 400,000
Iranians were surfing the uncensored Web.

The software was created not by Iranians, but by Chinese computer
experts volunteering for the Falun Gong, a spiritual movement that has
beem suppressed by the Chinese government since 1999. They maintain a
series of computers in data centers around the world to route Web
users’ requests around censors’ firewalls.

The Internet is no longer just an essential channel for commerce,
entertainment and information. It has also become a stage for state
control — and rebellion against it. Computers are becoming more
crucial in global conflicts, not only in spying and military action,
but also in determining what information reaches people around the
globe.

More than 20 countries now use increasingly sophisticated blocking and
filtering systems for Internet content, according to Reporters Without
Borders, a Paris-based group that encourages freedom of the press.

Although the most aggressive filtering systems have been erected by
authoritarian governments like those in Iran, China, Pakistan, Saudi
Arabia and Syria, some Western democracies are also beginning to
filter some content, including child pornography and other sexually
oriented material.

In response, a disparate alliance of political and religious
activists, civil libertarians, Internet entrepreneurs, diplomats and
even military officers and intelligence agents are now challenging
growing Internet censorship.

The creators of the software seized upon by Iranians are members of
the Global Internet Freedom Consortium, based largely in the United
States and closely affiliated with Falun Gong. The consortium is one
of many small groups developing systems to make it possible for anyone
to reach the open Internet. It is the modern equivalent of efforts by
organizations like the Voice of America to reach the citizens of
closed countries.

Separately, the Tor Project, a nonprofit group of anticensorship
activists, freely offers software that can be used to send messages
secretly or to reach blocked Web sites. Its software, first developed
at the United States Naval Research Laboratories, is now used by more
than 300,000 people globally, from the police to criminals, as well as
diplomats and spies.

Political scientists at the University of Toronto have built yet
another system, called Psiphon, that allows anyone to evade national
Internet firewalls using only a Web browser. Sensing a business
opportunity, they have created a company to profit by making it
possible for media companies to deliver digital content to Web users
behind national firewalls.

The danger in this quiet electronic war is driven home by a stark
warning on the group’s Web site: “Bypassing censorship may violate
law. Serious thought should be given to the risks involved and
potential consequences.”

In this cat-and-mouse game, the cat is fighting back. The Chinese
system, which opponents call the Great Firewall of China, is built in
part with Western technologies. A study published in February by
Rebecca MacKinnon, who teaches journalism at the University of Hong
Kong, determined that much blog censorship is performed not by the
government but by private Internet service providers, including
companies like Yahoo China, Microsoft and MySpace. One-third to more
than half of all postings made to three Chinese Internet service
providers were not published or were censored, she reported.

When the Falun Gong tried to support its service with advertising
several years ago, American companies backed out under pressure from
the Chinese government, members said.

In addition, the Chinese government now employs more than 40,000
people as censors at dozens of regional centers, and hundreds of
thousands of students are paid to flood the Internet with government
messages and crowd out dissenters.

This is not to say that China blocks access to most Internet sites;
most of the material on the global Internet is available to Chinese
without censorship. The government’s censors mostly censor groups
deemed to be state enemies, like the Falun Gong, making it harder for
them to reach potential members.

Blocking such groups has become more insidious as Internet filtering
technology has grown more sophisticated. As with George Orwell’s
“Newspeak,” the language in “1984” that got smaller each year,
governments can block particular words or phrases without users
realizing their Internet searches are being censored.

Those who back the ragtag opponents of censorship criticize the
government-run systems as the digital equivalent of the Berlin Wall.

They also see the anticensorship efforts as a powerful political
lever. “What is our leverage toward a country like Iran? Very little,”
said Michael Horowitz, a fellow at the Hudson Institute who advises
the Global Internet Freedom Consortium. “Suppose we have the capacity
to make it possible for the president of the United States at will to
communicate with hundreds of thousands of Iranians at no risk or
limited risk? It just changes the world.”

The United States government and the Voice of America have financed
some circumvention technology efforts. But until now the Falun Gong
has devoted the most resources, experts said, erecting a system that
allows the largest number of Internet users open, uncensored access.

Each week, Chinese Internet users receive 10 million e-mail messages
and 70 million instant messages from the consortium. But unlike spam
that takes you to Nigerian banking scams or offers deals on drugs like
Viagra, these messages offer software to bypass the elaborate
government system that blocks access to the Web sites of opposition
groups like the Falun Gong.

Shiyu Zhou, a computer scientist, is a founder of the Falun Gong’s
consortium. His cyber-war with China began in Tiananmen Square in
1989. A college student and the son of a former general in the
intelligence section of the People’s Liberation Army, he said he first
understood the power of government-controlled media when overnight the
nation’s student protesters were transformed from heroes to killers.

“I was so disappointed,” he said. “People believed the government,
they didn’t believe us.”

He decided to leave China and study computer science in graduate
school in the United States. In the late 1990s he turned to the study
of Falun Gong and then joined with a small group of technically
sophisticated members of the spiritual group intent on transmitting
millions of e-mail messages to Chinese.

Both he and Peter Yuan Li, another early consortium volunteer, had
attended Tsinghua University — China’s Massachusetts Institute of
Technology. Mr. Li, the son of farmers, also came to the United States
to study computer science, then joined Bell Laboratories before
becoming a full-time volunteer.

The risks of building circumvention tools became clear in April 2006
when, Mr. Li later told law enforcement officials, four men invaded
his home in suburban Atlanta, covered his head, beat him, searched his
files and stole two laptop computers. The F.B.I. has made no arrests
in the case and declined to comment. But Mr. Li thinks China sent the
invaders.

Early on, the group of dissidents here had some financial backing from
the International Broadcasting Bureau of the Voice of America for
sending e-mail messages, but the group insists that most of its effort
has been based on volunteer labor and contributions.

The consortium’s circumvention system works this way: Government
censorship systems like the Great Firewall can block access to certain
Internet Protocol addresses. The equivalent of phone numbers, these
addresses are quartets of numbers like 209.85.171.100 that identify a
Web site, in this case, google.com. By clicking on a link provided in
the consortium’s e-mail message, someone in China or Iran trying to
reach a forbidden Web site can download software that connects to a
computer abroad that then redirects the request to the site’s
forbidden address.

The technique works like a basketball bank shot — with the remote
computer as the backboard and the desired Web site as the basket. But
government systems hunt for and then shut off such alternative routes
using a variety of increasingly sophisticated techniques. So the
software keeps changing the Internet address of the remote computer —
more than once a second. By the time the censors identify an address,
the system has already changed it.

China acknowledges that it monitors content on the Internet, but
claims to have an agenda much like that of any other country: policing
for harmful material, pornography, treasonous propaganda, criminal
activity, fraud. The government says Falun Gong is a dangerous cult
that has ruined the lives of thousands of people.

Hoping to step up its circumvention efforts, the Falun Gong last year
organized extensive lobbying in Congress, which approved $15 million
for circumvention services.

But the money was awarded not to the Falun Gong consortium but to
Internews, an international organization that supports local media
groups.

This year, a broader coalition is organizing to push for more
Congressional financing of anti-filtering efforts. Negotiations are
under way to bring together dissidents of Vietnam, Iran, the Uighur
minority of China, Tibet, Myanmar, Cuba, Cambodia, Laos, as well as
the Falun Gong, to lobby Congress for the financing.

Mr. Horowitz argues that $25 million could expand peak usage to as
many as 45 million daily Internet users, allowing the systems to reach
as many as 10 percent of the Web users in both China and Iran.

Mr. Zhou says his group’s financing is money well spent. “The entire
battle over the Internet has boiled down to a battle over resources,”
he said. “For every dollar we spend, China has to spend a hundred,
maybe hundreds of dollars.”

As for the Falun Gong software, it proved a little too popular among
Iranians. By the end of last year the consortium’s computers were
overwhelmed. On Jan. 1, the consortium had to do some blocking of its
own: It shut down the service for all countries except China.